Preventive structure for preventing extraordinary deformation of a diaphragm of an oil hermetic type tensioner

Abstract

A tensioner for a chain or toothed belt which includes an oil reservoir. Oil contained in the oil reservoir is hermetically sealed by a diaphragm fixed to the oil reservoir by a plug. A pressurizing means is mounted between the diaphragm and the plug. The pressurizing means includes a compression spring and a bowl-shaped spring seat. A diaphragm is urged by the pressurizing means. A detent portion, extending upwardly from the diaphragm, is integrally formed on the surface of the diaphragm facing the atmosphere. The spring seat includes a recess at the central portion of the spring seat so that the detent portion of the diaphragm is engaged with the recess preventing free movement between the diaphragm and the pressurizing means.

What is claimed is: 
     
       1. An oil hermetic type tensioner, comprising: a cylinder;   a piston dividing an inside of said cylinder into a high-pressure chamber and a low-pressure chamber;   a housing defining an oil reservoir hydraulically communicating with said low-pressure chamber;   a diaphragm in said housing dividing said oil reservoir into an oil side and an atmosphere side and being operative to hermetically seal oil in said oil side of said oil reservoir;   means in said housing for pressurizing including a resilient body disposed in the atmosphere side of said reservoir, and means associated with said body for engaging said diaphragm on the atmosphere side thereof, said pressurizing means being operative to resist excessive deflection of said diaphragm; and   means for preventing free movement between said diaphragm and said pressurizing means including a detent projecting from said diaphragm on the atmosphere side thereof, and means associated with said diaphragm engaging means operative to retain said detent, whereby said detent is connected to said pressurizing means, so that free movement between said diaphragm and said pressurizing means is prevented.